Dr Willard Wigan fashioned and painstakingly put together more than 200 parts under a microscope to create the ornate work, which he hopes to take on a nationwide tour.
The artist, who created a tiny 24-carat gold crown for the Queen’s 2012 Diamond Jubilee, said of the previous work: “It was the proudest moment of my life but I’ve evolved and moved on since.
“I’ve improved, I’ve got so much better. I almost work as though my life depends upon it.
“Having autism has given me a superpower to be able to do things other people can’t do.”
The West Midlands-based sculptor was diagnosed with autism, which he describes as a blessing in disguise, at the age of 50.
He said: “My mother would tell me that autism is a diamond in a dustbin because humanity has a habit of throwing things away.
“And then all of a sudden the lid comes off the dustbin and they realise what was in there.
“ So I’m using this now as a message to humanity and a celebration to Her Majesty the Queen. This is the hardest thing I’ve ever done in my whole life.
“I think I need counselling now after doing this coach. But it’s taught me one thing – it’s taught me to train my attention span.”
Having worked for up to 17 hours a day for several weeks on the coach, the artist likens his work to “trying to put a pin through a bubble without bursting the bubble”.
He has also been working on a tiny model of Queen Elizabeth as a young woman, which has included painting with an eyelash attached to the end of a needle.
His previous works include the world’s smallest handmade BMX bike and a tribute to Albert Einstein.